We squashed migrations in the student djangoapp a while back.
This is the followup work to remove the migrations that were
squashed and to convert the squashed migration into a 'normal'
migration.
ARCHBOM-1177
Django 2.0 will make this field required for `ForeignKey` and `OneToOneFields`.
In previous versions the option defaulted to `models.CASCADE` when not
specified. This change should make the deprecation warnings in the current
Django version go away.
The migrations where also modified, but the changes should not cause a change in
the database schema since `models.CASCADE` was already the old default.
